Coffee Leaf Rust (Hemileia vastatrix) has recently been found in Hawaii.
This is a devastating fungal disease that has been found in most coffee growing areas of the world. It arose in Africa and moved to the Americas, now it is completing the circle, showing up in Hawaii. Coffee is the obligate host of this disease, meaning it only can reproduce on coffee. It needs coffee to survive and it needs to come into contact with another coffee plant for it to spread. It's most likely spread by humans moving infected coffee plant parts around – infected seed or the actual plants. It has caused turmoil in those countries where it has showed up, requiring frequent fungicidal sprays for its control. There is no cure for it at the moment, although farms have managed by planting more resistant varieties. There is no true resistance yet, however.
There is a small, but profitable growing coffee agriculture in California.
It hopefully can be protected from this disease. It really is dependent on travelers being aware of where they have been and what they carry with them. WE are our own worst enemies.
A recent alert has been posted by the University of Hawaii
Dear Growers and Friends,
Suspected coffee leaf rust has been reported on Maui.
Currently, HDOA is working to get a positive identification of this disease.
Growers, please scout your farms for any symptoms of coffee leaf rust. Here are my website and a poster that provides information and images of the disease on coffee trees.
If you suspect coffee leaf rust on any island, you can call HDOA's Plant Pest Control Branch at (808) 973-9525.
If you have questions about rust, you are also welcome to contact me at firstname.lastname@example.org. You can also text me at (415) 604-1511.
The HDOA memo can be found here.
A recent Atlantic article describes the disease and its impacts